JP3043698B2 - Method of manufacturing energy absorbing shaft - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an energy absorbing shaft used for, for example, a retractor of a seat belt for an automobile, and belongs to the technical field of manufacturing automobile parts and the like.

[0002]

2. Description of the Related Art A seat belt retractor in an automobile is connected to one end of a seat belt to urge the belt in a winding direction, and a sudden tensile load acts on the seat belt in a collision or the like. Sometimes
An energy absorbing shaft which is twisted by a torque based on the tensile load to absorb impact energy may be used.

As shown in FIG. 18, the shaft has polygonal engaging portions A1 and A2 provided at both ends to engage the torque input member and the fixing member, respectively, and a shaft at an intermediate portion therebetween. The intermediate shaft portion A3 is formed integrally with the portion A3, and the intermediate shaft portion A3 is appropriately formed when a large torque acts between the engaging portions A1 and A2 at both ends via the seat belt at the time of a collision of the vehicle. The material and the diameter or the torsional rigidity are set so as to be twisted.

[0004]

By the way, the energy absorbing shaft for the seat belt retractor exerts a large rigidity against a torque acting in the event of a collision of the vehicle, so that the occupant can pass through the seat belt. It is required that the seat belt be sufficiently twisted to loosen the seat belt in order to reliably support the vehicle and immediately after the operation of the air bag, in order to release the occupant to the air bag.

In other words, as shown by a solid line curve in FIG. 19, it is required to exhibit high rigidity to a certain limit with respect to an increase in input torque and hardly twist, and to easily twist if the torque exceeds the limit. It is done.

However, in the case of a conventional shaft in which the intermediate portion is formed into a shaft portion having a predetermined diameter by cutting (hereinafter, referred to as a conventional product), as shown by a broken line curve in FIG. At the moment of a collision, the airbag may start to twist from a relatively early stage, and may loosen prior to the operation of the airbag, and may not sufficiently withstand a large tensile load acting on the seat belt.

In order to cope with this, it is conceivable to impart the above-mentioned required characteristics by subjecting the conventional product to other processing such as quenching, but in this case, the manufacturing cost is increased.

Therefore, an energy absorbing shaft having such characteristics that it exhibits high rigidity and hardly twists up to a certain limit with respect to an increase in input torque, and easily twists if the torque exceeds the limit is easily manufactured at low cost. It is an object of the present invention to provide a manufacturing method capable of performing the above.

[0009]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized in that it is configured as follows.

That is, the invention according to claim 1 of the present application (hereinafter, referred to as the invention)
That the present invention) has an engagement portion which torque input member and the fixing member are respectively engaged in the two end portions, the middle portion of energy absorbing shaft which is a shaft portion which is twisted by the input torque from the input member The present invention relates to a manufacturing method, in which a wire made of a drawn metal having a circular cross section is used as a material, the wire is first reduced in diameter by drawing, and then the shaft is engaged with one end of the shaft. While forming the part and the engaging part of the other end of the shaft, at least for the shaft, only by cold forging the wire,
It is characterized in that it is formed to have a larger diameter than the dimension reduced by the drawing process.

According to the above configuration, the following operation can be obtained.

Namely, in the method of the present invention uses a wire of a metal which is drawn in a circular cross section as the material for the wire, first, it will be subjected to drawing, it is a metal
Wire with a circular cross section has a hardened surface during stretching
When the wire is reduced in diameter by drawing,
The surface becomes more hardened. Then, using this wire, at least the shaft part is larger than the dimension when the diameter was reduced by the above-mentioned drawing only by cold forging.
Since it is molded to a diameter, the hardened surface of the wire is not shaved or broken, and the hardened surface becomes thicker toward the inside, and the hardness around the shaft is higher than that of the predetermined thickness. A large high hardness layer will be formed.

Therefore, according to the invention of the present application , up to a certain limit with respect to an increase in the input torque, the high-hardness layer exhibits high rigidity due to withstanding this torque and hardly twists. The destruction of the high hardness layer produces an energy absorbing shaft that is easily twisted as a whole.

The wire is preferably made of steel, but may be made of stainless steel or another metal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an energy absorbing shaft according to an embodiment of the present invention will be described below.

The wire used in this embodiment is made of steel (J
IS display SWCH8R) is drawn by drawing several times from a large diameter to a small diameter in a cold state, and the wire diameter is 9.7 mm.
It has been. Further, this wire has a circular cross section and its surface is hardened by drawing.

First, as shown in FIG. 1, the wire is cut into a predetermined length to obtain a rod-like diameter D1.
Forms a material a of 9.7 mm.

Next, in the first cold forging step, as shown in FIG.
An intermediate material b having a reference shaft portion b1 of 32 mm and a small-diameter shaft portion b2 provided at one end thereof is formed.

Next, as shown in FIG. 3, the second cold forging step has a reference shaft portion c1 corresponding to the reference shaft portion b1 of the intermediate material b and a small-diameter shaft portion c2 at one end thereof. At the same time, an intermediate material c having a large-diameter portion c3 provided at the other end of the reference shaft portion c1 is formed.

Next, as shown in FIG. 4, a hexahedron having a reference shaft portion d1 and a small-diameter shaft portion d2 and shaping a large-diameter portion c3 of the intermediate material c by a third cold forging step. An intermediate material d having a portion d3 and a flange d4 adjacent to the portion d3 is formed.

Next, as shown in FIG. 5, a hexagonal body part d3 and a flange part d4 of the intermediate material d are formed by a fourth cold forging step, as shown in FIG. The intermediate material e having the engaging portion e3 thus formed is formed.

Further, in the fifth cold forging step, FIG.
As shown in the figure, the reference shaft portion f1, a small-diameter shaft portion f2 at one end thereof, and an engaging portion f3 at the other end thereof, and a large-diameter shaft is provided between the reference shaft portion f1 and the small-diameter shaft portion f2. The intermediate product f provided with the portion f4 is formed.

By performing post-processing as needed, as shown in FIG. 7, an intermediate shaft portion g1 and engaging portions g2, g3 formed in hexahedrons at both ends thereof are connected to one another. An energy absorbing shaft g as a final product having a small-diameter shaft portion g4 extending from the joint portion g3 and having a parallel two-faced portion g5 provided at the tip of the small-diameter shaft portion g4 is formed.

The post-processing may be performed by any processing such as forging, cutting, and pressing.

As described above, in this embodiment, the wire rod a of 9.7 mm is drawn to reduce the diameter of the reference shaft part b1 of 9.32 mm, and then cold forged four times. The reference shaft portion is gradually thickened, and the diameter D3 of the shaft portion g1 of the energy absorbing shaft g as the final product is formed to 9.5 mm. In this way, the wire rod whose surface is hardened is drawn by drawing. When the diameter is reduced, the surface is further hardened, and the wire is repeatedly subjected to cold forging, so that the hardened surface becomes thicker toward the inside as shown in FIG. High hardness layer g1 'around
Is formed.

FIG. 9 shows a hardness distribution in a cross section of the shaft portion g1 of the energy absorbing shaft g.

As shown in FIG. 9, in the case of the energy absorbing shaft g, a high hardness layer g1 'having a high hardness is formed over the range of X from the surface of the shaft portion g1.

Thus, the energy absorbing shaft g
A high-hardness layer g1 'having a higher hardness than the inside having a predetermined thickness is formed on the surface of the shaft portion g1. Therefore, torque is applied between the engaging portions g2 and g3 at both ends of the shaft portion g1. When actuated, the shaft g1 is hardly twisted until a large torque Y acts, as shown in FIG.

That is, in the case of the shaft g, the high hardness layer exhibits high rigidity by enduring this torque and hardly twists until the input torque increases to a certain limit. When the high hardness layer is broken, the whole is easily twisted.

Therefore, the energy absorbing shaft g
When used in the seat belt retractor for automobiles,
Exhibits great rigidity against the torque that is applied in the event of a car collision, and reliably supports the occupant via the seat belt. It acts to loosen the seat belt.

As a material of the wire, steel (JI
Although S display SWCH8R) is used, stainless steel or another metal may be used as the material.

Next, a manufacturing apparatus used for manufacturing the energy absorbing shaft according to this embodiment will be described.

As shown in FIG. 11, this manufacturing apparatus
A cold multi-stage forging device for forming an intermediate product of an energy absorbing shaft at a stage cold forging station X1 to X5, comprising a machine base 1, a cutter device (not shown), and die units 11 to 15 A plurality of punch units 21 to 25 are attached to a ram 2 which is reciprocatingly moved so as to approach and separate from the machine base 1 so as to face the die units 11 to 15 respectively.

First, as shown in FIG. 1, when a rod-shaped material a cut to a predetermined length from a wire is supplied to a first cold forging station X1 by a supply device, as shown in FIG. As the ram 2 advances, the punch unit 21 advances until it comes into contact with the die unit 11, and the material a is formed in the forming hole 32 of the die 32 held by the die holder 31.
a, the punch-side die 3 held by the punch holder 33
4 is held in a forming hole corresponding to the shape of the intermediate material b composed of the fourth forming hole 34a. Thereafter, the pressing plate 35 is further moved by the advance of the ram 2 so that the springs 36, 36 are moved.
Is pressed against the punch 37 while the punch 37 is driven into the forming hole 34a of the punch-side die 34. The reference shaft portion b1 is reduced in diameter, and the small-diameter shaft portion b2 provided at one end thereof. Intermediate material b having
(Shown in FIG. 2) is formed.

Then, the punch unit 21 retreats due to the retraction of the ram 2, and then the knockout pin 38 penetrating from the rear end face to the front end face of the die 32 projects toward the ram 2, thereby discharging the intermediate material b, and It is supplied to the second cold forging station X2.

Next, when the intermediate material b is supplied to the second cold forging station X2 by the supply device, the ram 2 advances to advance the punch unit 22 until it comes into contact with the die unit 12, as shown in FIG. Then, the intermediate material b corresponds to the shape of the intermediate material c composed of the forming hole 42a of the die 42 held by the die holder 41 and the forming hole 44a of the die 44 on the punch side held by the punch holder 43. It is held in the forming hole. After that,
As the ram 2 advances, the presser plate 45 is
The intermediate material c (shown in FIG. 3) is formed by abutting the punch 47 while compressing the 46 and driving the punch 47 into the forming hole 44 a of the punch-side die 44.

Then, the punch unit 22 is retracted by the retreat of the ram 2, and thereafter, the knockout pin 48 penetrating from the rear end face to the front end face of the die 42 projects toward the ram 2, thereby discharging the intermediate material c. It is supplied to the third cold forging station X3.

Next, when the intermediate material c is supplied to the third cold forging station X3 by the supply device, the punch unit 23 moves forward by the advance of the ram 2 as shown in FIG. Punch side die 5 held
The surface of the second forming hole 52a is in contact with the front end surface of the intermediate material c, and the intermediate material c is held by the die holders 53, 54 by the advancement of the punch-side die 52. The intermediate material d (shown in FIG. 4) is formed by being driven into 56a.

Then, the punch unit 23 retreats due to the retraction of the ram 2, and thereafter, the knockout pin 57 penetrating from the rear end face to the front end face of the die 56 projects toward the ram 2, thereby discharging the intermediate material d. It is supplied to the fourth cold forging station X4.

Next, when the intermediate material d is supplied to the fourth cold forging station X4 by the supply device, the punch unit 24 advances by the advance of the ram 2 shown in FIG. Forming hole 62a of punch 62
Surface comes into contact with the front end face of the intermediate material d, and the advance of the punch 62 causes the intermediate material d to move into the die holder 63,
Forming holes 6 of dies 65 and 66 held at
5a, 66a into the intermediate material e
(Shown in FIG. 5) is formed.

Then, the punch unit 24 retreats due to the retreat of the ram 2, and thereafter, the knockout pin 67 penetrating from the rear end face to the front end face of the die 66 protrudes toward the ram 2, thereby discharging the intermediate material e. It is supplied to the fifth cold forging station X5.

Next, when the intermediate material e is supplied to the fifth cold forging station X5 by the supply device, the punch unit 25 is advanced by the advance of the ram 2 shown in FIG. Forming hole 72a of punch 72
Is driven into the die with the surface of the intermediate material abutting on the front end surface of the intermediate material e.

In the process of pushing the intermediate material e into the front die 73 as the punch 72 moves forward,
The punches 72 come into contact with the plurality of divided die members 74.
The die member 74 is pressed together with the die members 74... 74ga together with the front die holder 76 into the mounting hole 1a of the machine base 1. At this time, the above-mentioned die members 74... 74 have a first tapered surface 74 a.
b is the first tapered surface 7 of the inner peripheral surface of the front die holder 76
6a and the second taper surface 76b, the springs 77 ... 77 for urging the dice members 74 ... 74 to expand the diameter are compressed to reduce the diameter as a whole.

The reduced-diameter die members 74...
The intermediate material e is gripped by the forming hole 73a constituted by 74, and in this state, the intermediate material e is driven into the forming hole 79a of the rear die 79 held by the rear die holder 78 by the advance of the punch 72. Intermediate product f
(Shown in FIG. 6) is formed.

Then, as shown in FIG. 17, the punch unit 25 retreats due to the retraction of the ram 2, and then the front die holder 76 grips the intermediate product f by the urging force of the compressed springs 75. 74 together with the held die members 74... 74 until they come into contact with the stopper plate 76. After that, a knockout pin 81 penetrating from the rear end face to the front end face of the rear die 79 protrudes toward the ram 2 so that the die member 7 is formed via the intermediate product f.
4. While 74 moves back in the front die holder 76,
These die members 74... 74 are expanded in diameter by the urging force of the compressed springs 77. And then,
The intermediate product f is discharged by the knockout pin 81 protruding toward the ram 2.

Then, by performing post-processing as needed, an energy absorbing shaft g (shown in FIG. 7) as a final product is formed.

According to such a manufacturing method , the diameter of the wire rod is reduced by the upper-stage station of the multi-stage cold forging machine, and thereafter, the connection between the shaft portion and one end thereof is performed by a plurality of stations from the next stage. A joining portion is formed, and furthermore, an engaging portion at the other end of the shaft portion is formed by a subsequent station provided with a split die, and the split die is enlarged in diameter from the diameter of the engaging portion. By taking out the product, the energy absorbing shaft having the engaging portions at both ends and having a high hardness layer formed around the shaft and having a hardness greater than the predetermined thickness is continuously and efficiently formed. It will be manufactured.

[0048]

As is evident from the foregoing description, in the method of the present invention, using a wire of a metal which is circular in cross section drawing as a material for the wire, first, it will be subjected to drawing, the metal Wire with a circular cross section consisting of
The surface is in a hardened state and the wire is reduced by drawing.
The surface becomes more hardened when the diameter is reduced. Then, using this wire, at least the shaft portion is reduced in diameter by the above-mentioned drawing by cold forging only.
Internal so formed into a larger diameter than the size, or hardened surface of the wire is cut, without or destroyed, this hardened surface becomes thicker towards the inside, of a predetermined thickness around the shaft portion Thus, a high-hardness layer having a higher hardness is formed.

Therefore, according to the present invention , the hardened layer exhibits high rigidity due to withstanding this torque and hardly twists up to a certain limit with respect to an increase in input torque. The destruction of the high hardness layer produces an energy absorbing shaft that is easily twisted as a whole.

[Brief description of the drawings]

FIG. 1 is a view showing a shape of a material before being processed by a manufacturing apparatus using a manufacturing method according to the present invention.

FIG. 2 is a view showing a shape of an intermediate material obtained by a first cold forging step of the manufacturing apparatus.

FIG. 3 is a view showing a shape of an intermediate material obtained by a second cold forging process of the manufacturing apparatus.

FIG. 4 is a view showing a shape of an intermediate material obtained by a third cold forging step of the manufacturing apparatus.

FIG. 5 is a view showing a shape of an intermediate material obtained by a fourth cold forging step of the manufacturing apparatus.

FIG. 6 is a view showing a shape of an intermediate product obtained by a fifth cold forging step of the manufacturing apparatus.

FIG. 7 is a view showing the shape of a final product obtained by post-processing.

FIG. 8 is an enlarged sectional view of a shaft portion of a final product.

FIG. 9 is a diagram showing the hardness from the surface to the center of the shaft of the energy absorbing shaft.

FIG. 10 is a diagram illustrating a relationship between an input torque and a torsion angle at a shaft portion of an energy absorbing shaft.

FIG. 11 is a schematic front view of a manufacturing apparatus using the manufacturing method according to the present invention.

FIG. 12 is a longitudinal sectional view of a first cold forging station of the manufacturing apparatus.

FIG. 13 is a longitudinal sectional view of a second cold forging station of the manufacturing apparatus.

FIG. 14 is a longitudinal sectional view of a third cold forging station of the manufacturing apparatus.

FIG. 15 is a longitudinal sectional view of a fourth cold forging station of the manufacturing apparatus.

FIG. 16 is a longitudinal sectional view showing a state where a die member of a fifth cold forging station of the manufacturing apparatus is reduced in diameter.

FIG. 17 is a longitudinal sectional view showing a state where a die member of a fifth cold forging station of the manufacturing apparatus is expanded in diameter.

FIG. 18 is a view showing a shape of a conventional energy absorbing shaft.

FIG. 19 is a diagram showing required characteristics and conventional characteristics of an energy absorbing shaft.

[Explanation of symbols]

 g Energy absorption shaft g1 Shaft g2, g3 Engagement

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Ogawa 12 Kirihara-cho, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd. (72) Inventor Masatoshi Shimizu 2-3-1 Edagawa, Koto-ku, Tokyo Nikka Sales Co., Ltd. (56) References JP-A-2-303648 (JP, A) JP-A-9-174190 (JP, A) JP-A-6-126371 (JP, A) JP-A-53-65428 (JP, A) JP-A-4-11571 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21J 1/00-13/14 B21K 1/00-29/00

Claims (1)

(57) [Claims] 1. Production of an energy absorbing shaft having an engaging portion at each end with which a torque input member and a fixing member are respectively engaged, and an intermediate portion serving as a shaft portion twisted by an input torque from the input member. A wire made of drawn metal having a circular cross section as a material, and firstly, the wire is reduced in diameter by drawing, and thereafter, an engagement portion between the shaft portion and one end of the shaft portion and the engagement portion are formed. Along with forming the engaging portion at the other end of the shaft portion, at least the shaft portion is formed into a larger diameter than the size reduced by the drawing process only by cold forging the wire. A method for producing an energy absorbing shaft, characterized in that: